This invention relates to electrochromic glazing and, more particularly, to such devices for safety glazing applications.
Electrochromic (EC) devices have many applications, some of them are automotive mirrors, car glazing including sunroofs, glazing for other transportation means such as boats, planes, trains, buses, etc., and for architectural glazing applications for interior and exterior uses. Briefly, EC devices are made by sandwiching an electrolyte between two coated substrates. Many examples of such devices are shown in U.S. Pat. No. 6,317,248 which is incorporated herein by reference. To operate these devices electrical power is applied across the electrolyte cross-section via the coatings on the substrate, so that a movement of the charged species (ions or polarized particles) takes place. These ions are transported via the electrolyte to the electrode surfaces for further reactions to take place which gives rise to color change or change in optical density. This change is varied reversibly at the discretion of the user. As used herein, the terms electrochromic devices are intended to also include devices in which polarized particles are not transported across the electrolyte for a color change, but instead simply re-orient themselves as in liquid crystal devices and suspended particle devices. In addition, other user controlled variable transmission devices employing similar principles of construction, i.e., an active material sandwiched between the two substrates, such as xe2x80x9cuser controlled photochromic devicesxe2x80x9d are also intended to be embraced by these terms. Such laminates may also be incorporated in window systems where additional glass elements are used (e.g., insulated glass units) where these additional elements may not be laminated.
While it is conventional practice in electrochromic devices to use a liquid electrolyte or a solid electrolyte, as shown, for example in U.S. Pat. Nos. 6,1534,306 and 5,856,211, such prior approaches have not resulted in an electrochromic device that exhibit safety characteristics common to conventional (non-electrochromic) laminated glasses such as those made by laminating polymeric sheets Safelex(trademark) (Solutia, Saint Louis, Mo.) or Butacite(trademark) (Dupont, Wilmington, Del.). Safety, in the context of applicable building industry and automotive industry standards, is defined not simply as preventing leakage of the electrolyte leakage from a broken laminate, but containment of the pieces of broken glass to avoid injury to the occupants in case of an impact.
One might suppose that it would be straight-forward to produce an electrochromic device that could exhibit the attributes of safety glazing by interposing between the substrates a polymeric sheet for glass lamination such as those made of polyurethane, PVC or polyvinylbutyral, including Butacite(trademark) from Dupont and Safelex(trademark) from Solutia. However, an electrochromic device requires chemically active contact between the electrolyte and the coated surfaces of the substrates which would be prevented by such ordinary plastic sheets without modification. Modification, such as addition of plasticizers by soaking could compromise their ability to impart safety attributes. Accordingly, it would be advantageous to achieve an electrochromic device that would exhibit the characteristics of impact-resistant safety glass. Moreover, a mandated use of tempered glass would not be satisfactory as it limits the type of transparent conductors and other coatings that can be used with electrochromic devices. Assembled EC devices made of glass substrates may be laminated with external sheets of polymeric material, such as Spallshield(trademark) (Dupont, Wilmington, Del.) to yield impact resistant laminates. However, these post processes increase cost and the scratch resistance of the polymeric sheets is usually not as good as glass.
In accordance with the principles of the present invention an electrochromic device is achieved that exhibits the characteristics of impact-resistant and scratch resistant safety glass without requiring the use of additional plastic laminates or tempered glass. We have discovered that such a device can be achieved by using a solid electrolyte sheet material, such as that described in EP 1056097, and by subjecting the assembly to heat and pressure in situ such that the electrolyte bonds to the treated surfaces of the glass substrate used for electrochromic devices with an adhesion of at least 1.8 kg/linear cm width, the electrolyte exhibiting a tensile strength of at least 5 kg/cm2.
Briefly, EP 1056097, discloses a solid electrolytic material having a polymeric binder selected from the group consisting of poly-acrylate, polystyrene, polyvinyl butyral, polyurethane, poly vinyl acetate, poly vinyl chloride and polycarbonate, a filler (such as polymer particles or pyrolitic silica, alumina, cerium oxide and zinc oxide), at least one dissociable salt (such as LiClO4, LiCF3SO3, LiN(CF3SO2)2, NaCF3SO3), at least one solvent for dissociating the salt (propylene carbonate, ethylene carbonate, gamma-butyro lactone, tetraglyme, sulfolane), and other additives (such as antioxidants and UV stabilizers).
To make the electrochromic safety glazing, the solid electrolytic sheet material is cut to size and placed between the two glass substrates having their coated surfaces (and for some types of EC devices, at least one of the surfaces is a reduced surface layer) facing the electrolytic sheet. The substrates are advantageously staggered in the busbar areas with the busbar on the two substrates along the two opposite edges, and the sheet preferably extends only to the coated area (i.e., does not extend on to the etched area or to the end of the substrate perimeter. The assembled device is then sealed in a vacuum bag (and a vacuum is pulled to degas). The assembled device is then subject to heating and pressure such as in an autoclave at 130xc2x0 C. and 200 psi for 1 hr with 45 min ramp time to adhere the polymeric electrolyte to the substrates. The pressure is maintained after the completion of the heating cycle and after the samples have cooled down to 60xc2x0 C. or lower.